In recent years, as a result of the increase in the operation speed of the PC, the popularization of the network infrastructure, and the increased capacity and reduced price of data storage, the chances of viewing documents and images, which used to be provided as printed matters on paper, as electronic information, which is easier.
As a display device for viewing such electrical information, conventional liquid crystal displays and CRTs, or recent light-emitting type displays such as organic EL displays are used. In particular, when the electronic information text is viewed, the display apparatus must be watched for a relatively long period of time. However, generally, the conventional display apparatus has a problem that its flicker causes human eyes to get tired.
A reflection type display using the external light is known as a display apparatus for solving the above-mentioned problem.
As a display method for realizing such reflection type display, there is much attention on the electrochemical display element using an electrodeposition method (hereinafter referred to as “ED method”) utilizing dissolution and deposition of metal or metal salt. The ED method has such advantages as a low driving voltage, simple cell structure, and excellent display quality with bright paper-like white and deep black.
The black/white density control in the ED method is performed by controlling the amount of deposited metal. The control is performed by, for example, changing a deposition voltage to be applied, or changing a time period for applying a constant deposition voltage.
For example, the Patent Document 1 discloses a method in which a time period for applying a deposition voltage to a pixel electrode is controlled to conduct a gray scale display and a method in which the deposition voltage is changed into a multi-valued voltage.